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Strabismus
(squint) (Aetiology (Idiopathic
Hydrocephalus,…
Strabismus
(squint)
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Pathophysiology
Defect
Many causes, often congenital, ocular disease or neurological disease (e.g. cranial nerves, CNS disease)
Mechanism
Both eyes not directed at an object at the same time,
one eye deviates from the midline
Classification
Eye position
Concomitant (non-paralytic; common): deviation doesn't vary with direction of gaze; often due to refractive error in one/both eyes
Non-comitant (rare): deviation varies with direction of gaze due to paralysis of extraocular muscles
Direction
Horizontal: esotropic (convergent) or exotropic (divergent)
Vertical: hypertropia (upward) or hypotropia (downward)
Combined, cyclotorsional (rotation)
Presence
Manifest: present when both eyes open and in use; one eye viewing object and other is deviated
Latent: present only when interruption of both eyes e.g. one covered
Accomodation
Accomodative: squint occurs with occomodation
Non-occomodative: squint unrelated to accomodation
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Diagnosis
Examination
CN exam
Nystagmus on eye movement (horizontal, vertical)
Any reduced acuity, focal signs
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Ophthalmoscopy
Light reflex (red reflex reduced in cataract, Rb due to leukocoria)
Papilloedema (raised ICP)
External eye examination
Any deformity, dysmorphic features (e.g. epicanthic folds)
Corneal light reflex test (pen torch light reflection on same place on cornea; if displaced, the child has a squint)
Cover test: manifest versus latent squint (drifts when covered)
Investigations
Bloods
FBC, CRP, U+E, LFT,
Autoimmune screen (MS, MG)
Genetic screen
Imaging
Slit lamp examination: cataracts, Rb
Formal visual field testing e.g. Humphrey
CT/MRI head: SOL, ischemia, hydrocephalus
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History
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POH
Bloods, scans, growth, gestation,
delivery, weight, complications
SH
Living arrangements, school/nursery,
occupation, smoking, alcohol
PC/HPC
Squint, poor vision,
developmental delay in children
Management
Conservative
Information, advice, support
Referral to local eye services (orthoptist, ophthalmologist)
Eye exercises (intermittent squints)
Medical
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Penalisation
Indication: ambylopia
MOA: deliberate blurring of good eye with
e.g. atropine drops, forcing use of ambylopic eye
Botulinum toxin
Indication: misaligned eyes despite other measures
MOA: paralyses one eye muscle to
cause paralysis and correct the squint
Surgical
Extraocular muscle repair
Indication: extraocular muscle damage/paralysis
MOA: insertion or shortening of a muscle
to correct the squinting eye
Complications
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Compensatory head postures
Abnormal posture e,g. head tilt
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Prognosis
Good if prompt treatment, as
correction can improve binocular vision
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